Crystalline silicate absorption at 11.1 μm: ubiquitous and abundant in embedded YSOs and the interstellar medium
Crystalline silicate absorption at 11.1 μm: ubiquitous and abundant in embedded YSOs and the interstellar medium
复制标题
11.1 μm 处的结晶硅酸盐吸收：在嵌入的 YSO 和星际介质中普遍存在且丰富
DOI：
--
复制
发表时间：
2020
期刊：
影响因子：
--
通讯作者：
M. Sterzik
中科院分区：
文献类型：
--
作者：
Tho Do;C. Wright;T. Fujiyoshi;A. Glasse;R. Siebenmorgen;R. G. Smith;B. Stecklum;M. Sterzik
利用4-8 μ望远镜上的几台仪器，我们在中红外(8-13 GHz)观测到了大量天体样本。它们包括几颗演化的恒星、多个嵌入的年轻恒星天体(YSO)或致密的H-II区域，以及几条穿过星际介质(ISM)的视线。后者是尘埃存在的地方--在演化的恒星流出和分子云中沉积之间，尘埃可能会被修改。在大多数物体中，我们不仅检测到非晶态硅酸盐的9.7 μm吸收特征，而且在11.1 μm附近还检测到第二个吸收带，其载流子是结晶镁橄榄岩。我们认为，结晶硅酸盐基本上普遍存在于ISM和恒星形成的早期阶段，是T-Tauri和HerBig恒星的演化先驱，在T-Tauri和HerBig恒星中经常发现这种硅酸盐。模拟表明，在大多数YSO、H-II区和ISM情况下，镁橄榄石的质量分数在1%-2% 之间，表明年轻相从ISM继承了它们的丰度。然而，几个来源显示出更强的特征(丰度≥3% Cent)。这表明，在恒星形成的早期，重要的过程，可能是通过热退火结晶而发生的。最耐人寻味的是首次在弥漫的ISM中检测到结晶硅酸盐。我们认为，我们观察到的丰度与注入ISM的10-20% 的结晶硅酸盐的质量分数以及普遍接受的反对它们被破坏的寿命是一致的，但只有在宇宙射线诱导的非晶化在几十亿年内微不足道的情况下才是一致的。
Utilizing several instruments on 4–8 m telescopes, we have observed a large sample of objects in the mid-infrared (8–13 μm). These comprise a few evolved stars, multiple envelopes of embedded young stellar objects (YSOs) or compact H-II regions, and several sightlines through the interstellar medium (ISM). The latter is where dust resides – and is potentially modified – between its formation in evolved stellar outflows and deposition in molecular clouds. In most objects, we detect not only the well-known 9.7 μm absorption feature of amorphous silicates but also a second absorption band around 11.1 μm whose carrier is attributed to crystalline forsterite. We propose that crystalline silicates are essentially ubiquitous in the ISM and earliest phases of star formation, and are evolutionary precursors to T-Tauri and Herbig stars where such silicates have been commonly found. Modelling shows that in most YSOs, H-II regions and ISM cases, the forsterite mass fraction is between 1 and 2 per cent, suggesting that the younger phases inherit their abundance from the ISM. However, several sources show much stronger features (abundances ≥3 per cent). This suggests that significant processing, perhaps crystallization by thermal annealing, occurs early on in star formation. Most intriguing is the first detection of crystalline silicate in the diffuse ISM. We propose that our observed abundance is consistent with a mass fraction of crystalline silicates of 10–20 per cent injected into the ISM, along with commonly accepted lifetimes against their destruction, but only if cosmic ray-induced amorphization is insignificant over a few Giga years.